Co Tyrone family-run firm Go Power has landed the biggest energy contract in Northern Ireland in a £58m deal with NI Water, ahead of plans to expand into the domestic market here.

Go Power will supply electricity to NI Water over the next two years.

It already supplies electricity to business customers, but now has plans to begin selling into Northern Ireland's domestic market - applying for a licence to compete here.

Go Power is continuing to grow and expand, with managing director Michael Loughran saying staff numbers are expected to grow from 40 to 150 by the end of the year.

It is part of the overall LCC Group and now enjoys around 20% market share within the Northern Ireland energy market.

But that's also set to grow on the back of this deal, and with the firm eyeing up the domestic market. And Go Power is already taking on big business clients in the Republic.

The deal makes Go Power the biggest supplier of electricity to large-user customers in NI, and the firm has plans to expand further - building a new site and adding jobs - according to Mr Loughran.

"This is very important to Go Power because they [NI Water] are the single biggest user in Northern Ireland.

"It's going to increase the major user market by over 10% and is of significance to us in terms of profile, because we have the biggest account in Northern Ireland."

"We already have some trial customers, but we are launching Go Power into the Republic of Ireland on October 1.

And the company has already landed some high-profile early stage customers such as Topaz.

"We are going to concentrate on the Northern Ireland market initially and then we are going to move into the commercial market in the Republic."

Mr Loughran said he was confident the firm could compete in an ever-increasingly crowded domestic market here.

"We are already under way for the domestic licence. Go [Power] has proved to be very efficient. We run a large volume, low margin business as efficiently as we can and we try to leave the products competitive. We are building a new facility for the electricity and we hope to reach 150 staff," he said.

The new deal will make up a big chunk of NI Water's annual budget, according to Ronan Larkin, director of finance and regulation for NI Water.

"We tendered the contract on the open market, and Go Power was successful," he said.

"It's one of our largest contracts. This contract will help run the assets, as well as looking to the environmental side. We want to make sure we can buy some energy that is green energy, and this fulfils that need as well."

Go Power recently rebranded to bring the firm's energy sales in line with its 'Go' petrol stations.

Go is enjoying a period of continuous growth within its gas and electricity provision. It now supplies electricity to some of Northern Ireland's biggest companies and government contracts, including Bombardier, Fane Valley and poultry giant Moy Park.

Welcoming the deal with NI Water, Regional Development Minister Danny Kennedy said it was a "major announcement".

"I think it represents good value for consumers, and for NI Water," he said.